The death of North Korean leader Kim Jong-Il has sent shockwaves around the world, but analysts played down fears of turbulence in the nuclear-armed nation and said a well-planned succession is under way.

Official announcements Monday on North Korean media, which revealed Kim had died two days previously at the age of 69, make it clear that his youngest son and heir apparent Jong-Un is firmly in power -- at least for now -- they said.

South Korea ordered its military to go on alert but as talk turned to the threat of war, President Lee Myung-Bak urged people to stay calm.

"I think there will be no immediate turbulence in the North's internal politics or foreign affairs," said Paik Hak-Soon of Seoul's Sejong Institute think-tank.

The North's media urged people to follow the leadership of Jong-Un, with the state news agency dubbing him the "great successor".

"All the party members, servicepersons and people should remain loyal to the guidance of respected Kim Jong-Un and firmly protect and further cement the single-minded unity of the party, the army and the people," it said.

Observers of the hermit state, which has long alarmed the international community with its nuclear capability and erratic manner, dispelled fears of an immediate power struggle or a military coup.

"This clearly indicates that Jong-Un is already firmly in power, and all key officials under Kim Jong-Il have decided for the past two days since Kim's death to support Jong-Un as the new leader," Paik said.

"The North's top guys have already sorted out everything, and the regime seems to be stable under the new leadership. I don't expect any major turbulence or power struggle within the regime in the foreseeable future."

"The Kim Jong-Un era has already started."

Little is known about Kim Jong-Un, the Swiss-educated young man who is now expected to extend the Kim dynasty into a third generation.

Aged in his late 20s, he had little public profile until his father suffered a stroke in 2008, forcing the succession plans to be accelerated.

In September 2010 he was handed senior ruling party posts and made a four-star general, despite his lack of any military experience. Since then, he has been constantly at his father's side.

Kim Jong-Il's only sister Kim Kyong-Hui and her husband Jang Song-Thaek, the country's unofficial number-two leader, are expected to act as his mentors and throw their weight behind the son's leadership.

Baek Seung-Joo of the Korea Institute for Defence Analyses said the North had fully prepared for Kim's death since his August 2008 stroke.

"For a while the military and Kim's family will try to uphold Kim Jong-Un as their leader and unite around him," Baek said.

But the young new leader, who comes into the job with little experience and a host of challenges including severe food shortages, is not expected to take on an ambitious agenda.

"Kim Jong-Un is not expected to seek any drastic policy change while trying to cement his leadership. He will try to share power or set up a strategic alliance with top military leaders," Baek said.

"A power struggle is possible in the future, creating an obstacle to his succession because Jong-Un did not secure full public support," he said, adding that a lack of popular backing made him vulnerable.

Kim Tae-Hyun, a professor at Seoul's Chung-Ang University, agreed that the son appears to be in charge with military and party backing -- and that the regime has a vested interest in maintaining the status quo.

Relations with South Korea have been icy since two deadly border incidents blamed on the North last year.

But Paik said the new leadership was unlikely to take a confrontational approach towards its old enemies the United States and South Korea for some time.

"It needs lots of aid and daily necessities to provide to its people to mark the major political anniversary in 2012," he said, referring to the 100th anniversary of the birth of founding president Kim Il-Sung.

News of the death came amid intensified diplomatic efforts to revive dormant six-nation negotiations on the North's nuclear programme.

"Regarding nuclear talks, the North will also likely take a more cooperative stance to get what they want," Paek said.

"They will probably come forward to renew negotiations with the US once the mourning period is over." (AFP)